A mining machine cutter typically has a plurality of replaceable teeth mounted in individual holders on the outside of the cutter. Each of these holders is welded to the cutter and carries a single cutter bit or tooth that is directed generally forward in a longitudinal direction of displacement of the cutter. The cutter can be shaped like a wheel, a frustocone, or a mushroom.
As described in U.S. Pat. No. 4,333,687 of Barnstorf the holder body is unitarily formed with feed passages that connect to a nozzle that is itself mounted o the holder and that is directed longitudinally generally forward in the displacement direction. Thus a fluid, either water or a water/air mixture, fed to the nozzle is emitted as a high-power spray that strikes whatever the cutter is engaging. This serves both to cool the cutter and to carry away material freed by it.
Even though the nozzle lies invariably in the wake of the cutter, that is behind it in its travel path, it is still in a fairly exposed position. Thus it is possible for particles freed by the cutter tooth to get into and plug the nozzle, and it is even possible under some circumstances for the nozzle and holder body to be directly abraded and badly damaged.
When this happens the nozzle is put out of commission. The only way to repair it is to take the cutter off and repair it in a shop. This obviously entails expensive down time.